Reticles or photomasks are used in lithographic processes for forming integrated circuits. For example, a pattern on a photomask is imaged and transferred onto a chemically amplified resist on a surface of the substrate. The patterned resist is then used to pattern one or more layers on a substrate to form desired features. Imaging errors occur due to limitations of light. For example, irregularities, such as line widths which are narrower or wider line widths than designed, may occur. Such irregularities are a result of proximity effect. To compensate for imaging errors, optical proximity correction (OPC) is employed.
Reticles, such as EUV reticles, used in lithography are generally formed by electron-beam (e-beam) patterning. Proximity effect correction of e-beam is based on monitoring of test patterns. However, conventional test patterns used for monitoring proximity effects have a narrow writing density variation range. Since e-beam dose is dependent on the writing density, conventional test patterns provide information only within a small dose variation range, limiting their effectiveness. Additionally, the CD or pitch provided by conventional test patterns is different from that of real production devices. Also, conventional test patterns are without pattern classification and bias compensation table.
From the foregoing discussion, it is desirable to provide monitoring patterns with wider writing density variation range.